1993 Chrysler Le Baron Idle control off causing bad timing?

The car idles rough. After it warms up it begins to lope between .75 and 1 rpm and starts a small knock but that gaoes away with a little gas. The rpms will also drop to .5 when shifting from drve to park now amd then. I have done a major tune up, replaced the fuel filter and the egr. Just dint know which way to go an this.
Thanks